1. Field of the Invention
The present disclosure generally relates to a filter configuration with at least one defected ground structure and, more particularly, to a filter configuration whose performance is improved through the use of at least one defected ground structure.
2. Description of the Related Art
Wireless communication technology has changed the way people exchange messages. In order to meet different demands of the users exchanging messages, the wireless transceivers with multiple modes and multiple bandwidths have become the essential components in the communication system. For example, since the wireless communication standards IEEE 802.11a and IEEE 802.11g operate at the bandwidths of 2.4 GHz and 5.2 GHz respectively, the wireless transceiver must include a band-pass filter in order to operate at both 2.4 GHz and 5.2 GHz. The band-pass filter is able to form a band-pass effect at each of the frequencies of 2.4 GHz and 5.2 GHz while excluding the signals at any frequency other than the above two frequencies, thereby achieving the multi-bandwidth transmission.
A band-pass filter may be formed by one or more step impedance resonators (SIR). For example, the band-pass filter may include two resonators. Each of the resonators usually has an electrical length of a half or a quarter of the wavelength, and includes a plurality of microstrip lines. As such, the filter can form a band-pass effect at a predetermined frequency by adjusting the coupling effects among the plurality of microstrip lines.
In general, the accuracy of the band-pass frequency and the decrement in the insertion loss have been the important indicators in evaluating the performance of the filter. However, the lengths or widths of the plurality of microstrip lines are often adjusted to change the band-pass frequency and to reduce the insertion loss of the conventional band-pass filter without taking the effect of the defected ground structure(s) into consideration. As a result, the accuracy of the band-pass frequency cannot be further improved, and the insertion loss cannot be further reduced.
In order to improve the performance of the conventional band-pass filter, it is necessary to provide a novel filter with at least one defected ground structure.